Retroviral arthritis: phenotypic analysis of cells in the synovial fluid of sheep with inflammatory synovitis associated with visna virus infection

Retroviral infections in sheep and goats: small ruminant lentiviruses and host interaction

Small ruminant lentiviruses (SRLV) are members of the Retrovirus family comprising the closely related Visna/Maedi Virus (VMV) and the Caprine Arthritis-Encephalitis Virus (CAEV), which infect sheep and goats. Both infect cells of the monocyte/macrophage lineage and cause lifelong infections. Infection by VMV and CAEV can lead to Visna/Maedi (VM) and Caprine Arthritis-Encephalitis (CAE) respectively, slow progressive inflammatory diseases primarily affecting the lungs, nervous system, joints and mammary glands. VM and CAE are distributed worldwide and develop over a period of months or years, always leading to the death of the host, with the consequent economic and welfare implications. Currently, the control of VM and CAE relies on the control of transmission and culling of infected animals. However, there is evidence that host genetics play an important role in determining Susceptibility/Resistance to SRLV infection and disease progression, but little work has been performed in small ruminants. More research is necessary to understand the host-SRLV interaction.

The immunobiology of viral arthritides

A large range of human viruses are associated with the development of arthritis or arthralgia. Although there are many parallels with autoimmune arthritides, there is little evidence that viral arthritides lead to autoimmune disease. In humans viral arthritides usually last from weeks to months, can be debilitating, and are usually treated with non-steroidal anti-inflammatory drugs, but with variable success. Viral arthritides likely arise from immunopathological inflammatory responses directed at viruses and/or their products residing and/or replicating within joint tissues. Macrophages recruited by monocyte chemoattractant protein-1 (MCP-1/CCL2) and activated by interferon, and proinflammatory mediators like tumour necrosis factor alpha, interferon gamma, interleukin-6 and interleukin-1beta appear to be common elements in this group of diseases. The challenge for new treatments is to target excessive inflammation without compromising anti-viral immunity. Recent evidence from mouse models suggests targeting MCP-1 or complement may emerge as viable new treatment options for viral arthritides.

Retroviral sequences in rheumatoid arthritis synovium

There are several relationships between retroviruses and cellular transformation, as well as retroviruses being involved in the development of autoimmune diseases. Retroviruses have been discussed as etiologic agents modulating or triggering certain pathways in the pathogenesis of rheumatoid arthritis (RA). However, none of the currently known retroviruses has been identified as specific for RA. Due to the unique properties of retroviruses, distinct experimental approaches can be used to detect retroviral activity in cells and tissues. Current research in RA using state-of-the-art molecular biology techniques includes both the search for exogenous and endogenous retroviral gene sequences in synovium of patients with RA.

Priming with tat-deleted caprine arthritis encephalitis virus (CAEV) proviral DNA or live virus protects goats from challenge with pathogenic CAEV

We previously reported that infection of goats with caprine arthritis encephalitis virus (CAEV) tat- proviral DNA or virus results in persistent infection, since the animals seroconverted and direct virus isolation from cultures of blood-derived macrophages was positive. In this study we wanted to determine whether goats injected with CAEV tat- proviral DNA or virus were protected against challenge with the pathogenic homologous virus and to investigate whether CAEV tat- was still pathogenic. All animals injected with CAEV tat- became infected as indicated by seroconversion and virus isolation. Challenge at 8 or 9 months postinfection demonstrated protection in four of four animals injected with CAEV tat- but did not in three of three mock-inoculated challenged goats. Challenge virus was undetectable in the blood macrophages of protected animals during a period of 6 or 10 months postchallenge. In two of four protected animals, however, we were able to detect the challenge wild-type virus by reverse transcriptase PCR on RNA directly extracted from synovial membrane cells surrounding the inoculation site. This result suggests that protection was achieved without complete sterilizing immunity. Animals injected with CAEV tat- and mock challenged developed inflammatory lesions in the joints, although these lesions were not as severe as those in CAEV wild-type-injected goats. These results confirm the dispensable role of Tat in CAEV replication in vivo for the establishment of infection and pathogenesis and demonstrate in another lentivirus infection model the efficacy of live attenuated viruses to induce resistance to superinfection.

The phenotype and phagocytic activity of macrophages during maedi-visna virus infection

Macrophages from maedi-visna virus (MVV) infected sheep have been shown to have an activated phenotype from sites of lesions in vivo. Here we have looked at the direct effect of virus infection on macrophage phenotype and activity in vitro by flow cytometry. There was no significant difference in the expression of several surface markers (CD4, CD8, MHC Class I, MHC Class II, lymphocyte function associated antigen(LFA)-1 and LFA-3) on monocyte-derived macrophages (MDM) by 5 days post MVV infection. In contrast the phagocytic activity of MVV-infected MDM for the yeast Candida utilis and erythrocytes was decreased by 5 days p.i. although the surface binding of erythrocytes was not affected. Interestingly, an activated phenotype was seen on alveolar macrophages (AM) from sheep with maedi (surface expression of MHC Class I, Class II and LFA-1 was increased), but there was no difference in the binding and phagocytosis of erythrocytes by these cells. However the binding and phagocytosis of the bacterium, Pasteurella hemolytica was increased with AM from MVV-infected sheep without lesions. Similarly there was no significant difference in the phagocytic and erythrocyte rosetting activity between fresh monocytes from MVV-infected and uninfected control sheep. Therefore the phenotype of macrophages taken from sites of lesions caused by MVV does not correspond to a direct effect by the virus on these cells or to particular activities of the macrophages.

The caprine arthritis encephalitis virus tat gene is dispensable for efficient viral replication in vitro and in vivo

Caprine arthritis encephalitis virus (CAEV) is a lentivirus closely related to visna virus and more distantly to other lentiviruses, such as human immunodeficiency virus. The genomes of visna virus and CAEV contain a tat gene encoding a protein able to weakly transactivate its own long terminal repeat, suggesting that transactivation may be a dispensable function for viral replication. Three different tat gene mutants of an infectious molecular clone of CAEV were used to study their replication after transfection or infection of primary goat synovial membrane cells and of blood-derived mononuclear cells or macrophages. Our results showed no difference between replication of the wild type and either the complete tat deletion mutant or the tat stop point mutant, whereas slower growth kinetics and lower levels of expression of the partial tat deletion mutant that of the wild type were obtained in these cells. Quantitative PCR and reverse transcription-PCR analyses of the different steps of a single replicative cycle revealed an identical pattern of retrotranscription, transcription, and viral production, whereas time course analysis demonstrated that the intracellular level of viral genomic RNA was affected by the partial tat deletion at later time points. We then compared the infectious properties of the wild-type and tat mutant viruses in vivo by direct inoculation of proviral DNAs into the joints of goats. All the animals seroconverted between 27 and 70 days postinoculation. Moreover, we were able to isolate tat mutant CAEV from blood-derived macrophages that was still able to infect synovial membrane cells in vitro. This study clearly demonstrates that the tat gene of CAEV is dispensable for viral replication in vitro and in vivo.

Immunoglobulin deposits in synovial membrane and cartilage and phenotype analysis of chondrocyte antigens in sheep infected with the visna retrovirus

Synovial membranes and cartilage slices from sheep infected with the maedi-visna retrovirus were examined for immunoglobulin deposits by immunohistology. Granular deposits of IgM and IgG were observed in the synovial membranes and upper layers of cartilage from about 40% of virus-infected sheep. These deposits were present in animals with subclinical joint disease, as well as those affected clinically. No significant deposits were found in the synovial membrane or cartilage from normal sheep. Infected animals tended to have reduced cartilage proteoglycan staining. Altered expression of MHC class II, CD1 and adhesion molecules by chondrocytes in cartilage from infected sheep with clinical or subclinical synovitis was observed suggesting that in vivo cell activation is an early event in cartilage degradation in these infections. Exogenously derived antiviral antibodies exhibited molecular mimicry towards chondrocyte antigens, but no in vivo evidence for cross-reactivity was observed. The results showed that IgM and IgG deposits, putatively containing either virus/antivirus immune complexes or autoantibodies were formed in the joints of sheep with clinical or subclinical synovitis. These immune deposits may initiate and perpetuate chronic inflammation with concomitant activation of chondrocytes leading to pannus formation and cartilage destruction.

Cytotoxic activity against maedi-visna virus-infected macrophages

The cell type predominantly infected by maedi-visna virus (MVV) is the macrophage, and we have looked at the ability of MVV-infected macrophages to interact with cytotoxic T lymphocytes (CTL), important effector cells against virus infections. MVV-specific CTL precursors were detected, after in vitro culture with MVV antigen and recombinant human interleukin-2, in peripheral blood lymphocytes of all MVV-infected sheep. MVV-infected monocyte-derived macrophages and alveolar macrophages were able to stimulate CTL activity in vitro and were targets for these activated CTL. The major effector cell population using MVV-infected macrophage targets was CD8+ lymphocytes, although another population, lymphokine-activated killer cells, may also have been involved. There was no direct cytotoxic activity found in alveolar lymphocytes from MVV-infected sheep without lung lesions.

Retroviruses and autoimmune rheumatic diseases

In autoimmune rheumatic diseases, retroviruses have been repeatedly discussed as important etiologic factors. However, despite a considerable amount of indirect evidence that retroviruses might indeed be involved in triggering or perpetuating autoimmune rheumatic diseases, clear cut direct evidence is still missing. Studies on arthropathies associated with HIV-1 or HTLV-1 infection as well as new experimental animal models like the Tax transgene mice and new data from the MLR/lpr mouse model might help to answer the questions how and by what mechanisms retroviral infection may lead to autoimmune rheumatic diseases. From data obtained in the MLR/lpr mouse it seems obvious that a potential link of retroviruses, apoptosis and autogenes to autoimmune diseases opens exciting new approaches to the study of rheumatic disease pathogenesis.

Phenotypic analysis of cells in bronchoalveolar lavage fluid and peripheral blood of maedi visna-infected sheep

A phenotypic analysis of bronchoalveolar lavage fluid (BALF) and peripheral blood (PB) cells in maedi visna virus (MVV)-infected sheep has been performed. The differential cell count in BALF from MVV-infected animals was characterized by a significant increase (P < 0.05) in lymphocytes and neutrophils. Lymphocyte phenotyping in BALF from MVV-infected sheep showed a significant decrease (P < 0.05) of CD4+ cells, a significant increase (P < 0.05) of CD8+ cells and a significant inversion (P < 0.001) of the CD4+/CD8+ ratio. CD5+ lymphocytes were also significantly decreased (P < 0.05). Gamma delta T cells and B cells did not differ significantly when compared with the controls. No correlation was observed between BALF and PB lymphocyte phenotypes. BALF macrophages from MVV-infected animals showed increased MHC class II expression and BALF lymphocytes from the same animals demonstrated up-regulation of LFA-1 and LFA-3 expression. These findings and their relationship with lentiviral pathogenesis are discussed.

Pathogenesis of central nervous system lesions in visna: cell-mediated immunity and lymphocyte subsets in blood, brain and cerebrospinal fluid

There are several indications that central nervous system (CNS) lesions in visna are immune-mediated and that cell-mediated immunity (CMI) may be of importance in the initiation of the lesions. To study the role of CMI in the pathogenesis of CNS lesions, five sheep were infected by intracerebral inoculation with visna virus and observed for 1 year. The following parameters were monitored at regular intervals: (1) neutralizing and ELISA antibodies; (2) visna virus-specific stimulation of lymphocytes from peripheral blood; (3) lymphocyte subpopulations in peripheral blood, cerebrospinal fluid (CSF) and brain at sacrifice. The CNS lesions were graded and compared with other parameters. The time course and titers of antibodies did not correlate with the severity of CNS lesions whereas the CMI did, indicating that CMI may play an important role in lesion development. The correlation of the number of CD8-positive cells in the CSF with the severity of lesions and the reversed ratio of CD4/CD8-positive cells in the diffusely infiltrated neuroparenchyma indicates that the CD8-positive T lymphocyte may be an important effector cell in the induction of CNS lesions.

Characterization of the lymphocytic alveolitis in visna-maedi virus-induced interstitial lung disease of sheep

In order to investigate the contribution of lymphocytes to interstitial lung disease in animals with visna-maedi infection, we studied in parallel bronchoalveolar cells and lung tissue from slaughter-house animals (n = 29) and from colostrum-deprived lambs transtracheally inoculated with field isolates of visna-maedi virus (n = 9) or saline (n = 6). Lymphocyte subpopulations were identified in bronchoalveolar lavage by immunofluorescence and flow cytometry analysis and in lung tissue using indirect immunohistochemistry. In infected animals a lymphocytic alveolitis containing CD4 and CD8 lymphocytes was observed. Peribronchovascular lymphoid nodules comprise mostly CD4 lymphocytes. Alveolar lymphocytes of both subsets displayed increased expression of MHC class II antigens in animals with naturally occurring maedi but not in experimentally infected ones. A sequential process of lymphocyte attraction and activation is likely to occur in vivo as part of the alveolitis.